<template>
  <scroll @scroll="scroll" :listenScroll="listenScroll" :probeType="probeType" ref="listview" class="listview" :data="data">
    <div>
      <ul>
        <li v-for="group in data" class="list-group" ref="listGroup">
          <h2 class="list-group-title">{{group.title}}</h2>
          <ul>
            <li @click="selectItem(item)" v-for="item in group.items" class="list-group-item">
              <img v-lazy="item.avatar" class="avatar">
              <span class="name">{{item.name}}</span>
            </li>
          </ul>
        </li>
      </ul>
    </div>
    <div class="list-shortcut" @touchstart="onShortcutTouchStart" @touchmove.stop.prevent="onShortcutTouchMove">
      <ul>
        <li v-for="(item, index) in shortcutList" class="item" :data-index="index" :class="{'current':currentIndex===index}">
          {{item}}
        </li>
      </ul>
    </div>
    <div class="list-fixed" v-show="fixedTitle" ref="fixed">
      <h1 class="fixed-title">{{fixedTitle}}</h1>
    </div>
    <div v-show="!data.length" class="loading-container">
      <loading></loading>
    </div>
  </scroll>
</template>
<script type="text/ecmascript-6">
import Scroll from 'base/scroll/scroll'
import Loading from 'base/loading/loading'
import {
  getData
} from 'common/js/dom'

const ANCHOR_HEIGHT = 18
const TITLE_HEIGHT = 30

export default {
  components: {
    Scroll,
    Loading
  },
  props: {
    data: {
      type: Array,
      default: []
    }
  },
  data() {
    return {
      scrollY: -1,
      currentIndex: 0,
      probeType: 1,
      diff: 0
    }
  },
  created() {
    this.probeType = 3
    this.listenScroll = true
    this.touch = {}
  },
  mounted() {
    this.$nextTick(() => {
      this.$refs.listview.refresh()
    })
  },
  computed: {
    shortcutList() {
      return this.data.map((group) => {
        return group.title.substr(0, 1)
      })
    },
    fixedTitle() {
      if (this.scrollY > 0) {
        return ''
      }
      return this.data[this.currentIndex] ? this.data[this.currentIndex].title : ''
    }
  },
  methods: {
    selectItem(item) {
      this.$emit('select', item)
    },
    onShortcutTouchStart(e) {
      let anchorIndex = getData(e.target, 'index')
      let firstTouch = e.touches[0]
      this.touch.y1 = firstTouch.pageY
      this.touch.anchorIndex = anchorIndex
        // this.$refs.listview.scrollToElement(this.$refs.listGroup[anchorIndex], 0)
      this._scrollTo(anchorIndex)
    },
    onShortcutTouchMove(e) {
      let firstTouch = e.touches[0]
      this.touch.y2 = firstTouch.pageY
      let delta = (this.touch.y2 - this.touch.y1) / ANCHOR_HEIGHT | 0
      let anchorIndex = parseInt(this.touch.anchorIndex) + delta
      this._scrollTo(anchorIndex)
    },
    refresh() {
      this.$refs.listview.refresh()
    },
    scroll(pos) {
      this.scrollY = pos.y
    },
    _calculateHeight() {
      this.listHeight = []
      const list = this.$refs.listGroup
      let height = 0
      this.listHeight.push(height)
      for (let i = 0; i < list.length; i++) {
        let item = list[i]
        height += item.clientHeight
        this.listHeight.push(height)
      }
    },
    _scrollTo(index) {
      console.log('index:', index)
      if (!index || index === 0) {
        return
      }
      this.scrollY = -this.listHeight[index]
      this.$refs.listview.scrollToElement(this.$refs.listGroup[index], 0)
    }
  },
  watch: {
    data() {
      setTimeout(() => {
        this._calculateHeight()
      }, 20)
    },
    scrollY(newY) {
      if (this.listHeight) {
        const listHeight = this.listHeight
          // 当滚动到顶部，newY>0
        if (newY > 0) {
          this.currentIndex = 0
          return
        }
        // console.log(newY)
        // 在中间部分滚动
        for (let i = 0; i < listHeight.length - 1; i++) {
          let height1 = listHeight[i]
          let height2 = listHeight[i + 1]
          if (-newY >= height1 && -newY < height2) {
            this.currentIndex = i
            this.diff = height2 - (-newY)
            return
          }
        }
        // 当滚动到底部，且-newY大于最后一个元素的上限
        this.currentIndex = listHeight.length - 2
      }
    },
    diff(newVal) {
      let fixedTop = (newVal > 0 && newVal < TITLE_HEIGHT) ? newVal - TITLE_HEIGHT : 0
      if (this.fixedTop === fixedTop) {
        return
      }
      this.fixedTop = fixedTop
      this.$refs.fixed.style.transform = `translate3d(0,${fixedTop}px,0)`
    }
  }
}
</script>
<style lang="scss">
@import "src/common/scss/variable";
@import "listview.scss";
</style>
